This invention relates generally to magnetic data storage devices that include patterned media, wherein each data bit is stored in a magnetically isolated block on the media, and more particularly to such devices with improved write clock synchronization.
Magnetic recording hard disc drives with bit patterned magnetic recording media have been proposed to increase the data density. In bit patterned media, the magnetic material on the disc is patterned into small isolated blocks or islands such that there is a single magnetic domain in each island or “bit”. The single magnetic domains can be a single grain or a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume. To produce the required magnetic isolation of the patterned blocks, the regions between the blocks are essentially nonmagnetic. Bit patterned media can solve the thermal decay problem that is expected to limit perpendicular recording products to less than 1 Tb/in2.
Disc drives typically use an actuator for positioning the read/write heads adjacent to the storage media. A servo control system receives servo positioning information read by the read/write heads from the data tracks, typically from equally-angularly-spaced servo sectors that extend generally radially across the tracks. The servo control system supplies control signals to the actuator to maintain the read/write heads on track and move them to the desired tracks for reading and writing of data. The servo sectors also contain servo timing marks (STMs) that indicate the start of the servo sectors. The STMs are often used as a reference clock signal for a write clock which controls the timing of the write pulses from the disc drive write head.
To assure that the disc drive write head magnetizes the islands on bit patterned media, the islands on the media must be positioned with an accurate period, and the write clock must be synchronized with the passing of the islands beneath the write head. Write clock synchronization ensures that a magnetic write field supplied by a transducer in the recording head will occur when the transducer is adjacent to one of the islands.
In storage systems that use bit patterned media, it is difficult to maintain adequate synchronization of the write clock with the bits on the media. While an error correcting code is typically used to correct corrupted bits, failure of write clock synchronization with the bits on the media may corrupt more bits than the error correcting code firmware can correct.